Generally, automated cartridge systems (ACS) provide a mechanism by which multiple users in a data processing system can have common access to multiple data storage subsystems, such as different multiple magnetic tape cartridge devices. In such a conventional system, physical data files generated by remote user computer systems are stored individually on different tape cartridges using an addressing arrangement. With such an arrangement, the potential loss of stored data is minimized if the system suddenly loses the ability to access a given tape cartridge as a result of hardware or tape failure, i.e., only the single data file stored on the inaccessible tape is likely to be lost because that is all that is stored on any individual tape cartridge.
However, recently efficiency in mass data access and storage utilization has been improved by employing a disk buffer between the remote users and a set of multiple volume cartridges (MVC) to create virtual data volumes in place of the actual transferred data files. Efficiency and utilization are increased in such a virtual volume arrangement because multiple virtual volumes can be selectively stored on a single cartridge to maximize space utilization. Such an arrangement is described in commonly owned copending U.S. patent application Ser. No. 09/110,217, filed on Jul. 8, 1988 now patentented with U.S. Pat. No. 6,094.605 and incorporated incorporated by reference herein.
While such a multiple virtual volume arrangement significantly improves utilization and throughput efficiency, the placement of multiple virtual volumes on a single cartridge has produced an undesirable side effect by increasing the amount of data at risk to loss if a MVC hardware or cartridge failure occurs. As a result, a need exists for an improved method for storing multiple virtual volumes which minimizes the amount of data which can be potentially lost without compromising the efficiency in space utilization otherwise provided.